very nice images.
Since you are starting on night photography, you might find a book of tips by a night photographer to be helpful. There are a number, but one that I have used is Mark Bowie's The Light of Midnight, available as an e-book here:
http://www.markbowie.com/shop/books. I took a workshop from him, and I found the book very useful even afterwards.
Everyone I know who does night photography sticks with base ISO and longer exposures for most shots. A cheap way to do this is to use the bulb setting and an inexpensive cable remote release, which you can buy very cheaply from eBay. I did that for a while, but I eventually splurged on an electronic release with a programmable timer. It allowed me to escape the mosquitoes, and it avoids the risk of accidentally shining a light when you look at your watch, etc.